Two-cylinder crankcase compression engine



TWO-CYLINDER CRANKCASE COMPRESSION ENGINE Filed May 13, 1952 2 She'ets-Sheet 1 INVENTOR.

flaw/ i ya/10392 01? Feb. 23, 1954 H. E. YARRINGTON 2,669,930

TWO-CYLINDER CRANKCASE COMPRESSION ENGINE Filed May 13, 1952 2 Sheets-Sheet 2 70 45 72 wwmfm,

Patented Feb. 23, 1954 TNT OFFICE TWO-CYLINDER CRANKCASE COMPRES- SION ENGINE Harold E. Yarrington, Eau Claire, Wis., assignor to National Presto Industries, Inc., a corporation of Wisconsin Application May 13, 1952, Serial No. 287,488

3 Claims.

. The present invention relates to connecting rods and particularly to connecting rods for twocycle internal-combustion engines.

In two-cycle internal-combustion engines having crankcase compression, an inlet valve admits a fuel-oil-air mixture to the crankcase of the engin on the compression or up stroke of the piston. On the power or down stroke of the piston, the mixture in the crankcase is compressed, and when the piston moves down far enough to uncover the intake port in the side of the cylinder block, the compressed mixtur flows from the crankcase through a transfer passage along the side of the block and into the cylinder through the uncovered intake port. To insure proper compression and flow of the mixture, it is desirable to keep the volume of the crankcase as small as possible so as to obtain as high a'pumping efficiency from the piston as possible.

In engines of the character defined, the trans fer passage on a single cylinder engine may be disposed along the upper side of the piston, the lower side of the piston, the low pressure side of the piston, or the high pressure side of the piston. In a two cylinder engine, the transfer pas" sage is usually located along either the low pressure side of the piston or the high. pressure side thereof. In clarification of the foregoing, the high pressure side of the piston is the side which is under pressure from connecting rod angularity during the power stroke, and th low pressure side is the side that is under pressure due to connecting rod angularity during the compression stroke. By providing the transfer pas sage along the high pressure side of the cylinder block, the high pressure side of the block is cooled by fuel transfer and more uniform'cylim der temperatures are obtained. In addition, with the transfer passage along the high pressure side, the circulation inside the crankcase I from the rotating crankshaft is then in such di motion as to tend to throw the fuel-air mixture outward into the transfer passage, thus theoretically increasing the horsepower output of the motor. Actual testing indicates that this effect is appreciable. From the foregoing, it will be apparent that with the transfer passage on the high pressure side, the connecting rod also swings through the crankcase towards the transfer passage and thus should also tend to move the fuel-air mixture towards the transfer passage.

It is an object of the present invention to ini crease the normal efficiency and horsepower out put of two-cycle internal-combustion engines by increasing the fuel transfer efficiency thereof. Specifically, it is an object of the invention to increase the tendency of the engine connecting rod to throw the fuel-air mixture toward the transfer passage in the engine block.

Another object of the present invention is to accomplish the foregoing specific object of the invention by providing an improved connecting rod for engines of the character defined.

Heretofore, engine connecting rods have been designed according to a set pattern wherein the rod comprises a pair of relatively enlarged bosses or heads and a relatively narrow shank of H-shaped cross-section connecting the heads. Very little attention has been paid to the connecting rod design, except that th sam fit the engine and be adapted to carry the necessary load. The improved connecting rod of the pres ent invention has some similarity to conventional rods except that the bosses and shank thereof are made as broad or as wide as possible. In particular, the crankshaft or crankpin boss of the rod is designed to fill as closely as possible the space between the crankshaft throws or webs and at least one web of the shank is broadened to substantially the same width as the boss. By increasing the width of the rod, the present invention provides for slight decrease in crankcas volume and for an increased fuel throwing characteristic. While the decrease in crankcase volume accomplished according to the invention is slight, the same is a step in the right direction so that the increased fuel throwing characteristic is not attained as a result of sacrificing crankcase compression.

In accordance with the foregoing, it is an obje'ct of the present invention to provide an improved connecting rod comprising a pair of bossespand a shank connecting the bosses, the shank having at least one web of a width substantially equal. to that of one of the bosses. It is preferred that a single wide web be provided and that the wide Web be disposed to the high pressure side of the piston so as to best enhance the fuel throwing characteristic of the rod.

A further object of the invention is the provision of an improved connecting rod of economical design, manufacture and assembly.

The present invention has the advantage, among others, of providing a definite horsepower increase, particularly at higher speeds, for twocycleinternal-combustion engines, without unduly increasing the cost of the engine.

Other objects'and advantages of the present invention will become apparent in the following throw of the crankshaft and for. the movement of the connecting rod, optimum fuelcompression conditions are not readily obtained. To provide for high engine efficiency, the eccentric throws forthe crankshaft include webs .32 of such voltime as to substantially fill the crankcase and thus decrease the volume thereof. As will be noted fromFigure 1, the webs 32 of the crank shaft throws fit closely within the confines of the crankcase I4 and the crankcases M are of relatively foreshortened height so that the crankshaft webs extend partially into the cylinder liners'to thus reduce crankcase volume to a minimum.

To further increase engine efiiciency, it will be noted from Figure 2 that if crankshaft and connecting rod rotation be in the direction indicated, the fuel-air mixture willbe forced, due to the rotation of the crankshaft and connecting rod,

in the direction of the intake passage 56. .To

maintain the relationship described, and as shown in Figure 2, the intake passage 56 and the intake port 542 are disposed to the high pressure side of the piston 46, that is, to'the side of the cylinder against which the piston exerts pressure during the power stroke of the piston. Due to the angularity of the connecting rod 38, the piston will exert pressure on opposite walls of the cylinder on the opposite strokes thereof. Considering Figure 2, connecting rod angularity is downward and to the right, on the power stroke, thus forcing the piston to the left and against the intake side of the cylinder.

While the foregoing features result in increased engine efiiciency, it is an object of the present invention to still further increase efliciency by effecting a slight decrease in crankcase volume and by substantially increasing the fuel throwing action of the crankshaft and connecting rod in an extremely economical and convenient manner. To accomplish this particular object, the present invention provides an improved connecting rod or an improved connecting rod feature adapted to be incorporated in conventional con.- necting rods. Referring to the drawings, the rod shown therein is conventional in substantially all respects and comprises the cylindrical wrist pin boss 49, the cylindrical crank pin boss 36 and the shank 42. The crank pin boss 36 is preferably formed integrally with the remainder of the connecting rod and is thereafter fractured or cut transversely so as to provide'a saddle portion 62 integral with the shank 42 and a cap 64 adapted to be detachably secured to the saddle 62 by means of a'pair of bolts 66 extending through the the webs generally being of approximately the size of the web indicated at 12 in Figure 3. According to the present invention, the connecting rod shank includes a broadened web of substantially the same width as the bosses of the rod so that the rod presents, when viewed in front elevation as shown in Figure 1, a substantially uniform width throughout its full length. ,The provision of the wide web 10 substantially increases engine efficiency as will be pointed. out hereinafter without presenting any substantial necting rod. ,The web I0 is preferably of a width substantially, equal to; the width of at least the crank pin boss of theconnecting rod so that the same, may be conformably received within the space between the webs 32 of the crankshaft throws and extends from the crank pin boss to: wardthe wrist pin boss. Preferably, the web 10 is continuous and merges with both bosses at its opposite ends. In cases where one of the connecting rod bosses is wider than the other, the web it at its opposite ends may be of substantially the same width asthe adjacent'boss and may taper or have other suitable configuration be: tween itsends. Preferably, the connecting rods formed according to the present invention have wrist pin bosses and crank pin bosses of substantially equal width andwebs of substantially the same width extending throughout the length of the connecting rod. If desired, the'rod may include two wide webs, such as the web l0, so that they connecting rod shank'is of substantially Ior Heshape in cross section. However, to decrease the amountof material required in the connect ing rod, to decrease the weight of the'rod and to preferable to provide a single web HIv so that the connecting rod shank is of generally T-shape .in

cross section, as is shown .in FigureB.

In construction, the crankpin boss Y36 and the lugs 58 thereof are preferably formed of a size to substantially fill the space. between the webs of the crankshaft throws and, as stated, theweb Hi is-formed of substantially the same width as the boss 35. Accordingly, the connecting rod of the present invention provides for a slight decrease in crankcase volume and a substantial increase in the fuel throwing characteristic of the rod. To further enhance these features, the present invention contemplates the provision of a groove M in each of the crankcases M to accommodate the connecting'rod. Referring to the drawings, 'it will be appreciated that portions of the crankpin boss 36 protrude from the margins of the crankshaft throws during operation of the engine. Rather than form the entire crankcase of a size to accommodate the rotation of the crankpin boss, the crankcase, in accordance with the present invention, is formed in the major portion thereof to accommodate onlythe crankshaft-webs,' and at "the portion thereof within which the crankpin boss moves,'agroove '14 is provided to accommodate the crankpin boss. Such construction results in a further slight decrease in crankcase volume and, in addition, provides a. trench or the like to concentrate the accumulation of fuel-air mixture in the path of rotation of- -the connecting rod. .155 will" be apparentfromFigure 2, the trench or groove :14 leads directly into the fuel transferpassage-SS;

In use and operation of the connecting rod of the present invention, the rod is mounted on the wrist pin 45 and the crank pin 34, asis shown in Figure 2, with the broad web 'w'thereof disposed to the high pressure side of'the piston, which, in accordance with the present invention,

is to the intake passage side of the crankcase and cylinder. widened web Hi of the improved connecting rod,

In operation, the enlarged or 

